EP0293545B1 - Method for the economical melting of glass and a glass melting furnace used therefor - Google Patents

Abstract

Raw materials are fed into the charging end of a melting section which is heated by electrodes in the glass bath. The melted charge is then clarified under fossil fuel burners in a clarifying section, where the highest temperature of the furnace is maintained, and homogenized in a homogenizing section from which the clarified melt is drawn. Flue gas from the clarifying section sweeps the surface of the melting section countercurrently to the charge and is then used to heat combustion air. Burners in the clarifying section are operated under air starved conditions to reduce nitrogen oxides, while burners in the melting section are operated with excess air to achieve complete combustion.

Description

The invention relates to an energy-saving process for melting glass in a glass melting furnace, in which the batch is melted in a melting part, refined in a refining part with a shallow bath depth adjoining the melting part, then homogenized in a subsequent homogenization part of increased bath depth and withdrawn therefrom, the The combustion gases are withdrawn and the batch input takes place at the beginning of the melting part and energy is supplied by electrodes under the batch input, with burners arranged in the refining part for supplying energy, with heat exchangers for energy exchange between the combustion gases and the combustion air supplied to the burners, and a glass melting furnace with one Melting part, a refining part adjoining the melting part with a small bath depth, an adjoining homogenization part of increased bath depth, which is provided with an outlet for the glass, with one other at the beginning of the melting part Ordered device for feeding the batch and arranged under the batch application electrodes for supplying energy, with burners arranged in the refining section for supplying fossil energy, with heat exchangers for exchanging energy between the combustion gases and the combustion air supplied to the burners.

Glass melting furnaces, although they work with recuperators or regenerators, generally have the disadvantage of a relatively low efficiency. This is not due to the lack of insulation in the glass troughs, but rather because the exhaust gas heat considerably exceeds the thermal energy required to preheat the combustion air. There are limits to an increase in the temperature of the combustion air, since this makes the heat exchange very expensive is, but especially disadvantageously increases the concentration of toxic NO _x .

Various attempts have already been made to use the excess heat in the exhaust gas sensibly, including the batch preheat before placing in the glass melting pan. However, these attempts were unsuccessful because the pre-melting of some batch components can already occur as a result of the heating, as a result of which the heat exchange surfaces stick together and, on the other hand, when the exhaust gas comes into direct contact with the batch, in addition to the pre-melting of certain components, segregation also occurs or certain batch components are taken along , whereby the dust content in the exhaust gas is increased inadmissibly or very complex dust filters are required.

From EP-A1-0 230 492, a glass melting furnace with an improved efficiency is already known, which is achieved in that the burner gases sweep over a large area of the batch layer floating on the melt and are thereby cooled. The remaining and already reduced thermal energy is then released into the combustion air in heat exchangers.

A disadvantage of this furnace, however, is that batches can get into the refining part and into the homogenization part and the glass quality is therefore insufficient.

Another glass melting furnace is known from US Pat. No. 3,198,618, in which the combustion gases sweep over the batch layer floating on the melt. Here, too, there is disadvantageously no refining part in which the glass is adequately refined, but the use of bubblers promotes a vertical circulating flow which allows contaminated glass or glass mixed with a mixture to get into the work tub.

In contrast, it is an object of the invention to provide a method for melting glass and a glass melting furnace, which no longer have the disadvantages mentioned, the furnace used having a considerably improved efficiency compared to known furnaces should, however, be economical to produce and in which there are in particular low NO _x concentrations and a lower dust content in the exhaust gas, without the need to control high-temperature components in the furnace or for heat exchange.

The upper furnace temperature and the temperature in the heat exchangers used (recuperators) are said to be even lower than in the conventional, known furnaces.

In addition to the advantages mentioned, the furnace according to the invention should be economically producible and reliable to operate, and if need be an extensive exchange of fossil and electrical energy should be possible.

This object is achieved according to the invention in a method of the type mentioned at the outset in that the predominant supply of melt energy is carried out by burners of fossil fuel in the refining part, the flue gases sweep over the melt part in countercurrent to the batch, are drawn off close to the batch task and the melt part on the surface by a flow coming from the refining part is flowed through in countercurrent to the batch and that measures are present which absorb the flame radiation from the refining part at its boundary and above the melting part, as a result of which the space above the melt is divided into zones of different temperatures in which the highest The temperature in the refining part is present.

The process is advantageously carried out in such a way that in the refining part (zone I) with the highest temperature the burners for reducing nitrogen oxide formation with a deficit of air and in the part (zone II) lower temperature as seen from the flue gas flow the burners arranged on the inflow are run with excess air to complete the combustion.

In the case of a glass melting furnace of the type mentioned at the outset, the object of the invention is achieved in such a way that, in order to form the hot flow as a countercurrent to the batch movement, the bottom of the melting part falls from the refining part to the batch input and the roof of the furnace between the refining part (zone I) and your melting part (Zone II) has at least one radiation protection wall which extends up to just above the bath surface.

Furthermore, electrodes arranged beneath the batch advantageously have the effect that a descending flow forms next to them towards the refining part, which deflects the hot glass flow downward in the melting part, as a result of which the backflow running at the bottom is amplified towards the refining part.

The heat transfer by radiation from the burner part, which reduces the efficiency, is advantageously prevented by the radiation protection walls provided between the refining and melting parts and in the melting part.

The particular advantage of the method and glass melting furnace according to the invention is that the exhaust gases are cooled to 800-1000 ° C while preheating the batch lying on the glass bath until they emerge from the tub space and the recuperators reduce the air in counterflow to approx Can heat up to 700 ° C.

Obviously, the glass melting furnace according to the invention, in connection with the method for its operation, is able to solve the problems in a particularly advantageous manner Wise to solve for the first time. The invention The principle here is to apply the mixture to the glass bath and preheat it there by the exhaust gas and thereby cool the exhaust gas to such an extent that the remaining energy can be used almost completely to heat the combustion air. The liquid remains in the glass and the setting of an optimal flow field in the batch preheating area of the tub is ensured by the addition of comparatively small amounts of electrical energy.

Further advantageous embodiments of the invention are mentioned in subclaims 3 to 5 and 7 to 10.

Figur 1

einen Längsschnitt durch eine Glaswanne gemäß der Erfindung,

Figur 2

einen Horizontalschnitt durch eine Wanne ähnlich Figur 1 und

Figur 3

einen Horizontalschnitt durch eine andere Ausführungsform einer erfindungsgemäßen Wanne.

Exemplary embodiments of the invention are explained in more detail below with reference to drawings. Show it:

Figure 1

2 shows a longitudinal section through a glass trough according to the invention,

Figure 2

a horizontal section through a tub similar to Figure 1 and

Figure 3

a horizontal section through another embodiment of a tub according to the invention.

According to the figures, the glass melting furnace according to the invention consists of an elongated, rectangular trough with a refining part 2 and a melting part 3, which merge into one another. The refining part 2 is the flat trough part in which the burners 20 are arranged, which are used to burn oil or gas.

The trough also has a transverse wall 16 on the burner side, a transverse wall 17 and longitudinal walls 18 on the batch side. The upper furnace is formed by a ceiling 1. The melting part base is designated by 9.

Bottom electrodes 6 are arranged in the melting part (zone II) 3 and prevent the glass bath from freezing in this area, in particular in the direct area of the batch. The freezing is further prevented in that a surface flow is set within the melting part 3, which continuously conveys highly heated glass from the refining part 2, which has been heated by the burners 20, into the area of the batch feed.

The batch application takes place in a conventional manner over the entire width of the transverse wall 17.

In particular, the tub is constructed in accordance with conventional technology, as is also described in the applicant's older applications, so that a further description can be dispensed with. This applies in particular to the design of the walls, the vault, the floor, the burner, the electrodes and the outlet 19 at the end of the homogenization part 2a remote from the batch task and to the design of the exhaust gas outlet openings 22 directly next to the batch task.

A radiation protection wall 5 is arranged in the interior of the tub at the end of the refining part 2 on the task side, which extends from the ceiling to just above the bath surface 4 and prevents radiation from reaching the melting part 3. As is known, the greatest part of the energy is transmitted by radiation at high chamber temperatures and it is therefore essential to the invention to concentrate the energy supplied by the burners 20 in the refining part 2.

Since further considerable amounts of radiation from the bath surface and in particular from the radiation protection wall 5 to the feed side are effective, the melting part 3 has a further radiation protection wall 7 in the vicinity of the batch task and between the protective walls 5 and 7 a further protective wall 8. With this arrangement it is reliably prevented that radiant energy is used to heat the batch, but this should be done practically exclusively by the exhaust gas which flows from the refining part 2 through the melting part 3 to the exhaust gas outlet openings 22.

The floor 9 can optionally have a threshold 14 at the end of the refining part 2 on the input side. What is essential, however, is the evenly sloping bottom toward the batch application, which sets a flow pattern in which hot glass flows back to the batch support on the bath surface and, in conjunction with the bottom electrodes 6, prevents the glass from freezing there. The bottom in the refining part 2 is arranged horizontally.

The exhaust gas, which has cooled to approx. 900 ° C, is fed into the recuperator after it leaves the tank, from which it emerges at a temperature of approx. 150 - 250 ° C. At this temperature, the energy inherent in the exhaust gas has largely been transferred to the combustion air.

In the recuperators, the combustion air is preheated from the normal temperature to a temperature of approx. 700 ° C. by the cooling exhaust gas and then fed to the burners 20 via pipes. The combustion that takes place due to the relatively low air temperatures has the advantage that the flame temperatures are relatively low and therefore higher concentrations of NO _x cannot occur. The exhaust gas is not only cooled to a great extent, but also has extremely low concentrations of NO _x , so that the glass melting furnace according to the invention can also be operated in areas with low emission values, for example in cities, especially since the use of a dust filter due to the low exhaust gas temperatures is easily possible.

From the operation of the trough, it is important that the melting part 3 serves only for batch preheating in its end on the feed side and that the batch melts substantially only at the end of the melting part 3 on the burner side, the refining part 2 then refining the glass before it passes through a bottom outlet 19 is withdrawn in a known manner.

A number of "bubblers" are arranged in the refining part 2, which can introduce air through the ground. This air causes a strong circulation of the glass in the refining part 2, if necessary with the aid of bottom electrodes, so that only a very small temperature gradient can occur within the refining part from top to bottom. This ensures that the surface of the floor reaches temperatures of about 1550 - 1560 ° C, the arch temperature of the vault above the refining part 2 not exceeding 1580 ° C. The temperatures in the melting part 3, on the other hand, are considerably lower, from 1100 to 1300 ° C. from the batch feed to the refining part 2.

In the homogenization part 2a, the glass is homogenized with cooling, so that an optimal temperature stratification is established, which prevents circulating currents and thus the introduction of contaminants into the outlet 19.

The radiation protection walls 5, 7 and 8 set a gas velocity above the batch of approx. 10-15 m / s, which in addition to the radiation heat transfer also allows a certain convective heat transfer. The radiation protection walls are constructed, for example, according to right-angled arches as with large dog house arches.

The electrical energy supplied can furthermore be selected in relation to the energy supplied by the burners in such a way that the NO _x mass flow does not exceed the permissible values. With a higher proportion of the electrical energy, the NO _x mass flow decreases and increases with a reduction in the proportion.

The glass melting furnace according to the invention can be produced economically, since inexpensive refractory material can be used in the batch application part due to the lower temperatures.

It is in the essence of the invention that the entire glass melting furnace, the lines for the exhaust gas and for the heated combustion air are strongly insulated. Nevertheless, it is surprising for the person skilled in the art that the specific energy consumption can be reduced to the previously unattained value of 3100 - 3400 kjoules / kg glass.

In the refining section designated as Zone I, the burners are operated with a deficit of air, so that nitrogen oxide formation (NO _x formation) practically does not occur since the combustion is incomplete. The fuel gases then enter Zone II, namely the melting part, and there in the flow-related beginning of Zone II, in which the temperature is already around 150 ° C lower than in Zone I, the burners are used to achieve complete combustion of the feed Hydrocarbons run with excess air so that a loss of efficiency is avoided. Due to the much lower temperature prevailing here, practically no NO _x occurs, so that the exhaust gases are practically NO _x -free when entering the atmosphere. The glass melting furnace according to the invention can therefore also advantageously work in densely populated areas.

It is also essential that with a mixture of a high proportion of broken glass and a remainder of the usual batch is driven, so that it is possible to operate the furnace with cheap raw materials. Due to the increasing quantities of recycled waste glass, which cannot yet be separated according to color, fragments with different oxidation potential get into the melting tank. When glasses with different oxidation potentials react with each other, a strong foam forms on the surface of the bath, which reflects the flame radiation and greatly impedes the transfer of heat into the glass bath.

This foam can be greatly reduced by reducing the fire, so that the new tub works better than conventional tubs under the unfavorable conditions when large quantities of waste glass are used.

Claims (10)

1. Economical method of melting glass in a glass-melting furnace, in which the raw mixture is melted in a melting unit (3), is refined in a shallow refining unit (2) adjacent to the melting unit (3), and is subsequently homogenized in and, thereafter, drawn off an homogenizing unit (2a) of greater depth lying next to the refining unit (2), whereby the exhaust gas vent and the raw mixture input lie at the top-end of the melting unit (3) and, under the raw mixture input, energy is introduced via electrodes(6) and burners (20) for introducing energy are disposed in the refining unit (2), with heat exchangers (10, 11) for transferring energy between the exhaust gases and the combustion air to be fed to the burners (20),
   characterized in that
   the preponderent amount of the energy for melting originates from the introduction of heat energy by fossil fuel burners (20) in the refining unit (2), that the exhaust gases flow over the melting unit (3) in the opposite direction to that of the raw mixture current, escape close to the raw mixture input and the gas flow moving in the opposite direction to the raw mixture current flows over the entire surface (4) of the melting unit (3) and that provisions are made to absorb at its boundary and above the melting unit (3) the flame radiation from the refining unit (2), whereby the space above the hot glass melting is subdivided in zones with differing temperatures, among which the highest temerature is present in the refining unit (2).
2. Method according to patent claim 1, characterized in that in the refining unit (2) (zone I) with the highest temperature, the burners (20) are operated with reduced quantities of air, in order to decrease the formation of nitric oxides and in the adjacent unit (zone II), as seen from the perspective of the exhaust gas flow, with its lover temperature, the burners (20) disposed at the inflow are operated with excess air to complete the combustion.
3. Method according to claim 2, characterized in that the temperature in zone II is set at approximately 150°C lower than that in zone I.
4. Method according one of the claims 1 to 3, characterized in that the raw mixture contains a large portion of recycled glass.
5. Method according to claim 4, characterized in that, after their exit from the heat exchangers (10, 11), the exhaust gases flow through the old glass and are cooled to a temperature equivalent to the condensation point of their components.
6. Glass-melting furnace for the implementation of the method according to claims 1 to 5 with a melting unit (3), a shallow refining unit (2) adjacent to the melting unit (3) and a homogenizing unit (2a) with a deeper vat, the whole connected to the refining unit (2) and furnished with an glass outlet (19), with a device for introducing the raw mixture situated at the top end of the melting unit (3) and, ordered below the raw mixture input, elec tordes (6) for introducing energy, with burners (20) in the refining unit (2) for introducing energy, with heat exchangers (10, 11) for energy exchange between the fuel exhaust gases and the combustion air to be fed into the burners, characterized in that, in order to develop a hot gas flow as a countercurrent to the movement of the raw mixture at the bottom of the melting unit (9) from the refining unit (2) towards the raw mixture input point and that the ceiling (1) of the furnace between the refining unit (2) (zone I) and the melting unit (3) (zone II) is furnished with at least one heat radiation shield extending to a point immediately above the operasting surface.
7. Glass-melting furnace according to claim 6, characterized in that the evenly inclined bottom extends over the whole length of the melting unit (3) and the bottom of the refining unit (2) is horizontal.
8. Glass-melting furnace according to either of the claims 6 or 7, characterized in that the melting unit (3) is furnished with at least one heat radiation shield (7).
9. Glass-melting furnace according to one of the claims 6 to 8, characterized in that the heat exchangers are recuperators equipped with both a high temperature and a low temperature section (10 and 11).
10. Glass-melting furnace according to claim 7, characterized in that the bottoms (9) of the refining unit (2) and the melting unit (3) are furnished with means of injecting air (bubblers).

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